Impeller for catheter pump

ABSTRACT

An impeller for a pump is disclosed herein. The impeller can include a hub having a fixed end and a free end. The impeller can also have a plurality of blades supported by the hub. Each blade can have a fixed end coupled to the hub and a free end. The impeller can have a stored configuration and a deployed configuration, the blades in the deployed configuration extending away from the hub, and the blades in the stored configuration being compressed against the hub.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 17/013,066, filed on Sep. 4, 2020, which is a Continuation ofU.S. patent application Ser. No. 16/026,995, filed on Jul. 3, 2018, andissued as U.S. Pat. No. 10,765,789, which is a Continuation of Ser. No.15/589,366, filed on May 8, 2017, and issued as U.S. Pat. No.10,039,872, which is a Continuation of U.S. patent application Ser. No.15/142,522, filed on Apr. 29, 2016, and issued as U.S. Pat. No.9,675,740, which is a Continuation of U.S. patent application Ser. No.14/401,096, filed on Nov. 13, 2014 and issued as U.S. Pat. No.9,327,067, which claims the benefit of priority to P.C.T. ApplicationNo. PCT/US2013/040809, filed on May 13, 2013, which claims the benefitof priority to U.S. patent application Ser. No. 13/802,570, filed onMar. 13, 2013 and issued as U.S. Pat. No. 8,721,517, which claims thebenefit of priority to U.S. Provisional Patent Application No.61/667,875, filed on Jul. 3, 2012, and U.S. Provisional PatentApplication No. 61/646,827, filed on May 14, 2012, all of which arehereby incorporated by reference herein. Any and all applications notlisted above for which a foreign or domestic priority claim isidentified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

This application is directed to pumps for mechanical circulatory supportof a heart. In particular, this application is directed to variousimplementations of an impeller that can be used in a catheter pump.

Description of the Related Art

Heart disease is a major health problem that has high mortality rate.Physicians increasingly use mechanical circulatory support systems fortreating heart failure. The treatment of acute heart failure requires adevice that can provide support to the patient quickly. Physiciansdesire treatment options that can be deployed quickly andminimally-invasively.

Intra-aortic balloon pumps (IABP) are currently the most common type ofcirculatory support devices for treating acute heart failure. IABPs arecommonly used to treat heart failure, such as to stabilize a patientafter cardiogenic shock, during treatment of acute myocardial infarction(MI) or decompensated heart failure, or to support a patient during highrisk percutaneous coronary intervention (PCI). Circulatory supportsystems may be used alone or with pharmacological treatment.

In a conventional approach, an IABP is positioned in the aorta andactuated in a counterpulsation fashion to provide partial support to thecirculatory system. More recently minimally-invasive rotary blood pumphave been developed in an attempt to increase the level of potentialsupport (i.e. higher flow). A rotary blood pump is typically insertedinto the body and connected to the cardiovascular system, for example,to the left ventricle and the ascending aorta to assist the pumpingfunction of the heart. Other known applications pumping venous bloodfrom the right ventricle to the pulmonary artery for support of theright side of the heart. An aim of acute circulatory support devices isto reduce the load on the heart muscle for a period of time, tostabilize the patient prior to heart transplant or for continuingsupport.

There is a need for improved mechanical circulatory support devices fortreating acute heart failure. Fixed cross-section ventricular assistdevices designed to provide near full heart flow rate are either toolarge to be advanced percutaneously (e.g., through the femoral arterywithout a cutdown) or provide insufficient flow.

There is a need for a pump with improved performance and clinicaloutcomes. There is a need for a pump that can provide elevated flowrates with reduced risk of hemolysis and thrombosis. There is a need fora pump that can be inserted minimally-invasively and provide sufficientflow rates for various indications while reducing the risk of majoradverse events. In one aspect, there is a need for a heart pump that canbe placed minimally-invasively, for example, through a 15 FR or 12 FRincision. In one aspect, there is a need for a heart pump that canprovide an average flow rate of 4 Lpm or more during operation, forexample, at 62 mmHg of head pressure. While the flow rate of a rotarypump can be increased by rotating the impeller faster, higher rotationalspeeds are known to increase the risk of hemolysis, which can lead toadverse outcomes and in some cases death. Accordingly, in one aspect,there is a need for a pump that can provide sufficient flow atsignificantly reduced rotational speeds. These and other problems areovercome by the inventions described herein.

SUMMARY

There is an urgent need for a pumping device that can be insertedpercutaneously and also provide full cardiac rate flows of the left,right, or both the left and right sides of the heart when called for.

In one embodiment, an impeller for a pump is disclosed. The impeller cancomprise a hub having a proximal end portion and a distal end portion. Ablade can be supported by the hub. The blade can have a fixed endcoupled to the hub and a free end. Further, the impeller can have astored configuration when the impeller is at rest, a deployedconfiguration when the impeller is at rest, and an operationalconfiguration when the impeller rotates. The blade in the deployed andoperational configurations can extend away from the hub. The blade inthe stored configuration can be compressed against the hub. The bladecan include a curved surface having a radius of curvature. The radius ofcurvature can be larger in the operational configuration than when theimpeller is in the deployed configuration.

In another embodiment, a percutaneous heart pump is disclosed. The pumpcan comprise a catheter body and an impeller coupled to a distal endportion of the catheter body. The impeller can comprise a hub. A bladecan be supported by the hub and can have a front end portion and a backend portion. The blade can include a ramped surface at the back endportion. A sheath can be disposed about the catheter body and can have aproximal end and a distal end. The distal end of the sheath can beconfigured to compress the blade from an expanded configuration to astored configuration when the distal end of the sheath is urged againstthe ramped surface of the blade.

In yet another embodiment, a method for storing an impeller isdisclosed. The method can comprise urging a sheath against a rampedsurface of a back end of a blade of an impeller. The impeller can haveone or more blades. Further, the impeller can have a storedconfiguration and a deployed configuration. Each blade in the storedconfiguration can be compressed against a hub of the impeller. Eachblade in the deployed configuration can extend away from the hub. Themethod can further comprise collapsing the blade against the hub to urgethe impeller into the stored configuration.

In another embodiment, a percutaneous heart pump system is disclosed.The system can comprise an impeller disposed at a distal portion of thesystem. The impeller can be sized and shaped to be inserted through avascular system of a patient. The impeller can be configured to pumpblood through at least a portion of the vascular system at a flow rateof at least about 3.5 liters per minute when the impeller is rotated ata speed less than about 21,000 revolutions per minute.

In another embodiment, a method of pumping blood through the vascularsystem of a patient is disclosed. The method can comprise inserting animpeller through a portion of the vascular system of the patient to aheart chamber. The method can further include rotating the impeller at aspeed less than about 21,000 revolutions per minute to pump bloodthrough at least a portion of the vascular system at a flow rate of atleast about 3.5 liters per minute.

In yet another embodiment, an impeller configured for use in a catheterpump is disclosed. The impeller can comprise a hub having a distalportion, a proximal portion, and a diameter. The impeller can alsoinclude a blade having a fixed end at the hub and a free end. The bladecan have a height defined by a maximum distance between the hub and thefree end. A value relating to a ratio of the blade height to the hubdiameter can be in a range of about 0.7 to about 1.45.

In another embodiment, a percutaneous heart pump system is disclosed.The system can comprise an impeller disposed at a distal portion of thesystem, the impeller sized and shaped to be inserted into a vascularsystem of a patient through a percutaneous access site having a sizeless than about 21 FR. The impeller can be configured to pump blood inthe vascular system at a flow rate of at least about 3.5 liters perminute.

In another embodiment, a percutaneous heart pump system is disclosed.The system can include an impeller comprising one or more blades in asingle row. The impeller can be disposed at a distal portion of thesystem. The impeller can be sized and shaped to be inserted through avascular system of a patient. The impeller can be configured to pumpblood through at least a portion of the vascular system at a flow rateof at least about 2.0 liters per minute when the impeller is rotated ata speed less than about 21,000 revolutions per minute.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the subject matter of this applicationand the various advantages thereof can be realized by reference to thefollowing detailed description, in which reference is made to theaccompanying drawings in which:

FIG. 1 illustrates one embodiment of a catheter pump configured forpercutaneous application and operation;

FIG. 2 is a plan view of one embodiment of a catheter adapted to be usedwith the catheter pump of FIG. 1;

FIGS. 3A-3C illustrate the relative position of an impeller blade and aninner surface of an impeller housing in an undeflected configuration;

FIG. 4 shows the catheter assembly similar to that of FIG. 2 in positionwithin the anatomy;

FIGS. 5A-5F are three-dimensional (3D) perspective views of an impelleraccording to one embodiment;

FIG. 6 is a 3D perspective view of an impeller according to anotherembodiment;

FIG. 7 is a 3D perspective view of an impeller according to yet anotherembodiment;

FIG. 8 is a side view of an impeller according to another embodiment;

FIGS. 9A-9E are side views of impellers according to variousembodiments;

FIG. 10A is a side view of an impeller according to yet anotherembodiment;

FIG. 10B is a 3D perspective view of the impeller of FIG. 10A;

FIG. 11 is a side view of an impeller according to another embodiment.

FIG. 12 is a schematic, side cross-sectional view of an impeller havinga hub and one or more blades disposed within a housing.

FIG. 13 is a chart plotting flow rate versus motor speed for theimpellers illustrated in FIGS. 10A-10B and 9E.

FIG. 14 is a chart plotting flow rate versus motor speed for an impellersimilar to or the same as the impeller of FIGS. 10A-10B, as compared tovarious conventional microaxial, rotary pumps.

More detailed descriptions of various embodiments of components forheart pumps useful to treat patients experiencing cardiac stress,including acute heart failure, are set forth below.

DETAILED DESCRIPTION

This application is directed to apparatuses for inducing motion of afluid relative to the apparatus. In particular, the disclosedembodiments generally relate to various configurations for an impellerdisposed at a distal portion of a percutaneous catheter pump. Forexample, FIGS. 1-4 show aspects of an exemplary catheter pump 10 thatcan provide high performance flow rates. The exemplary pump 10 includesa motor driven by a controller 22. The controller 22 directs theoperation of the motor 14 and an infusion system 26 that supplies a flowof infusant or infusate in the pump 10. A catheter system 80 that can becoupled with the motor 14 houses an impeller within a distal portionthereof. In various embodiments, the impeller is rotated remotely by themotor 14 when the pump 10 is operating. For example, the motor 14 can bedisposed outside the patient. In some embodiments, the motor 14 isseparate from the controller 22, e.g., to be placed closer to thepatient. In other embodiments, the motor 14 is part of the controller22. In still other embodiments, the motor is miniaturized to beinsertable into the patient. Such embodiments allow the drive shaft tobe much shorter, e.g., shorter than the distance from the aortic valveto the aortic arch (about 5 cm or less). Some examples of miniaturizedmotors catheter pumps and related components and methods are discussedin U.S. Pat. Nos. 5,964,694; 6,007,478; 6,178,922; and 6,176,848, all ofwhich are hereby incorporated by reference herein in their entirety forall purposes.

FIG. 4 illustrates one use of the exemplary catheter pump 10. A distalportion of the pump 10, which can include an impeller assembly 92, isplaced in the left ventricle (LV) of the heart to pump blood from the LVinto the aorta. The pump 10 can be used in this way to treat patientswith a wide range of conditions, including cardiogenic shock, myocardialinfarction, and other cardiac conditions, and also to support a patientduring a procedure such as percutaneous coronary intervention. Oneconvenient manner of placement of the distal portion of the pump 10 inthe heart is by percutaneous access and delivery using the Seldingertechnique or other methods familiar to cardiologists. These approachesenable the pump 10 to be used in emergency medicine, a catheter lab andin other non-surgical settings. Modifications can also enable the pump10 to support the right side of the heart. Example modifications thatcould be used for right side support include providing delivery featuresand/or shaping a distal portion that is to be placed through at leastone heart valve from the venous side, such as is discussed in U.S. Pat.Nos. 6,544,216; 7,070,555; and US 2012-0203056A1, all of which arehereby incorporated by reference herein in their entirety for allpurposes.

FIG. 2 shows features that facilitate small blood vessel percutaneousdelivery and high performance, including up to and in some casesexceeding normal cardiac output in all phases of the cardiac cycle. Inparticular, the catheter system 80 includes a catheter body 84 and asheath assembly 88. The impeller assembly 92 is coupled with the distalend of the catheter body 84. The exemplary impeller assembly 92 isexpandable and collapsible. In the collapsed state, the distal end ofthe catheter system 80 can be advanced to the heart, for example,through an artery. In the expanded state, the impeller assembly 92 isable to pump blood at high flow rates. FIGS. 2-4 illustrate the expandedstate. The collapsed state can be provided by advancing a distal end 94of an elongate body 96 distally over the impeller assembly 92 to causethe impeller assembly 92 to collapse. This provides an outer profilethroughout the catheter assembly 80 that is of small diameter, forexample, to a catheter size of about 12.5 FR in various arrangements.Although various expandable impellers are disclosed herein (e.g.,impellers having a stored configuration and a deployed configuration),it should be appreciated that the principles described below may also beapplicable to impellers that may not be expandable or collapsible. Forexample, the impeller parameters described herein may also be applicableto fixed diameter impellers in some arrangements.

In some embodiments, the impeller assembly 92 includes a self-expandingmaterial that facilitates expansion. The catheter body 84 on the otherhand preferably is a polymeric body that has high flexibility. When theimpeller assembly 92 is collapsed, as discussed above, high forces areapplied to the impeller assembly 92. These forces are concentrated at aconnection zone, where the impeller assembly 92 and the catheter body 84are coupled together. These high forces, if not carefully managed canresult in damage to the catheter assembly 80 and in some cases renderthe impeller within the impeller assembly 92 inoperable. Robustmechanical interface, are provided to assure high performance.

The mechanical components rotatably supporting the impeller within theimpeller assembly 92 permit high rotational speeds while controllingheat and particle generation that can come with high speeds. Theinfusion system 26 delivers a cooling and lubricating solution to thedistal portion of the catheter system 80 for these purposes. However,the space for delivery of this fluid is extremely limited. Some of thespace is also used for return of the infusate. Providing secureconnection and reliable routing of infusate into and out of the catheterassembly 80 is critical and challenging in view of the small profile ofthe catheter body 84.

When activated, the pump 10 can effectively increase the flow of bloodout of the heart and through the patient's vascular system. In variousembodiments disclosed herein, the pump 10 can be configured to produce amaximum flow rate (e.g. low mm Hg) of greater than 4 Lpm, greater than4.5 Lpm, greater than 5 Lpm, greater than 5.5 Lpm, greater than 6 Lpm,greater than 6.5 Lpm, greater than 7 Lpm, greater than 7.5 Lpm, greaterthan 8 Lpm, greater than 9 Lpm, or greater than 10 Lpm. In variousembodiments, the pump can be configured to produce an average flow rateat about 62 mmHg during operation of greater than 2 Lpm, greater than2.5 Lpm, greater than 3 Lpm, greater than 3.5 Lpm, greater than 4 Lpm,greater than 4.5 Lpm, greater than 5 Lpm, greater than 5.5 Lpm, orgreater than 6 Lpm. In various embodiments, the pump can be configuredto produce an average flow rate of at least about 4.25 Lpm at 62 mmHg.In various embodiments, the pump can be configured to produce an averageflow rate of at least about 4 Lpm at 62 mmHg. In various embodiments,the pump can be configured to produce an average flow rate of at leastabout 4.5 Lpm at 62 mmHg.

Various aspects of the pump and associated components are similar tothose disclosed in U.S. Pat. Nos. 7,393,181, 8,376,707, 7,841,976,7,022,100, and 7,998,054 and U.S. Pub. Nos. 2011/0004046, 2012/0178986,2012/0172655, 2012/0178985, and 2012/0004495, the entire contents ofwhich are incorporated herein for all purposes by reference. Inaddition, this application incorporates by reference in its entirety andfor all purposes the subject matter disclosed in each of the followingconcurrently filed applications: U.S. patent application Ser. No.13/802,556, which corresponds to attorney docket no. THOR.072A, entitled“DISTAL BEARING SUPPORT,” filed on Mar. 13, 2013; U.S. PatentApplication No. 61/780,656, which corresponds to attorney docket no.THOR.084PR2, entitled “FLUID HANDLING SYSTEM,” filed on Mar. 13, 2013;U.S. patent application Ser. No. 13/801,833, which corresponds toattorney docket no. THOR.089A, entitled “SHEATH SYSTEM FOR CATHETERPUMP,” filed on Mar. 13, 2013; U.S. patent application Ser. No.13/801,833, which corresponds to attorney docket no. THOR.092A, entitled“CATHETER PUMP,” filed on Mar. 13, 2013; and U.S. patent applicationSer. No. 13/802,468, which corresponds to attorney docket no. THOR.093A,entitled “MOTOR ASSEMBLY FOR CATHETER PUMP,” filed on Mar. 13, 2013.

Blade & Impeller Configurations

With reference to FIGS. 3A-3C, an operative device of the pump caninclude an impeller 300 having one or more blades 303. The one or moreblades 303 can extend from an impeller hub 301. It can be desirable toincrease the flow rate of the heart pump while ensuring that theimpeller 300 can be effectively deployed within a subject. For example,an impeller can include one or more blades 303 that are configured to beinserted into a subject in a stored, or compressed, configuration. Whenthe impeller 300 is positioned in the desired location, e.g., a chamberof a subject's heart as shown in FIG. 4, the blade(s) 303 of theimpeller 300 can self-expand into a deployed or expanded configuration,in which the blade(s) 303 extends radially from a hub 301.

As shown in FIGS. 3A-3B, the impeller 300 can be positioned within acannula or housing 202. A free end of the blades 303 can be separatedfrom the wall W of the housing 202 by a tip gap G. The housing 202 canalso have a stored, or compressed configuration, and a deployed orexpanded configuration. The housing 202 and impeller 300 may deploy fromthe stored configurations from within a sheath or sleeve (not shown)into the expanded configuration. In such implementations, the sheath orsleeve can keep the blade(s) 303 and the housing 202 compressed untilthe blade(s) 303 and housing 202 are urged from within a storage cavityof the sheath or sleeve. Once the blade(s) 303 are released from thestorage cavity of the sheath, the blade(s) 303 can self-expand to adeployed configuration using strain energy stored in the blades 303 dueto deformation of the blade(s) 303 within the sheath or sleeve. Theexpandable housing 202 may also self-deploy using stored strain energyafter being urged from the sheath.

In the stored configuration, the impeller 300 and housing 202 have adiameter that is preferably small enough to be inserted percutaneouslyinto a patient's vascular system. Thus, it can be advantageous to foldthe impeller 300 and housing 202 into a small enough storedconfiguration such that the housing 202 and impeller 300 can fit withinthe patient's veins or arteries. In some embodiments, therefore, theimpeller 300 can have a diameter in the stored configurationcorresponding to a catheter size between about 8 FR and about 21 FR. Inone implementation, the impeller 300 can have a diameter in the storedstate corresponding to a catheter size of about 9 FR. In otherembodiments, the impeller 300 can have a diameter in the storedconfiguration between about 12 FR and about 21 FR. For example, in oneembodiment, the impeller 300 can have a diameter in the storedconfiguration corresponding to a catheter size of about 12 FR or about12.5 FR.

When the impeller 300 is positioned within a chamber of the heart,however, it can be advantageous to expand the impeller 300 to have adiameter as large as possible in the expanded or deployed configuration.In general, increased diameter of the impeller 300 can advantageouslyincrease flow rate through the pump. In some implementations, theimpeller 300 can have a diameter corresponding to a catheter sizegreater than about 12 FR in the deployed configuration. In otherembodiments, the impeller 300 can have a diameter corresponding to acatheter size greater than about 21 FR in the deployed or expandedconfiguration.

In various embodiments, it can be important to increase the flow rate ofthe heart pump while ensuring that the operation of the pump does notharm the subject. For example, increased flow rate of the heart pump canadvantageously yield better outcomes for a patient by improving thecirculation of blood within the patient. Furthermore, the pump shouldavoid damaging the subject. For example, if the pump induces excessiveshear stresses on the blood and fluid flowing through the pump (e.g.,flowing through the cannula), then the impeller can cause damage toblood cells, e.g., hemolysis. If the impeller damages a large number ofblood cells, then hemolysis can lead to negative outcomes for thesubject, or even death. As will be explained below, various bladeparameters can affect the pump's flow rate as well as conditions withinthe subject's body.

Overview of Various Embodiments

Various embodiments of an impeller for use in a heart pump are disclosedherein. In particular, FIGS. 5A-11 illustrate different configurationsfor an impeller 300-300J. Each of the disclosed impellers 300-300J canbe defined by several different characteristics or parameters that canadvantageously improve flow rate while achieving healthy outcomes in apatient. Further, various properties or characteristics of the disclosedimpellers may assist in storing and/or deploying the impeller intoand/or out from an outer sleeve. Each figure may only illustrate a fewof the characteristics of the impeller for ease of illustration.However, it should be appreciated that each illustrated impeller may beassociated with all of the characteristics or properties disclosedherein. For example, some figures may illustrate only a few angles orother geometric or structural properties of the impeller, but it shouldbe appreciated that all the impellers disclosed herein may be associatedwith the disclosed characteristics or properties (see, e.g., the examplevalues given in Tables 1 and 2).

In order to improve patient outcomes, it can be advantageous to providea heart pump capable of pumping blood at high flow rates whileminimizing damage to the blood or the patient's anatomy. For example, itcan be desirable to increase flow rate while reducing the motor speed,as higher motor speeds are known to increase the hemolysis risk.Furthermore, for percutaneous insertion heart pump systems, it can beadvantageous to make the diameter of the impeller and the cannula assmall as possible for insertion into the patient's vasculature.Accordingly, the various impeller embodiments disclosed herein canprovide high flow rate while maintaining a diameter small enough forinsertion into the patient's vasculature and while reducing the riskthat the patient's anatomy and blood are damaged during operation of thepump.

For some or all of the impellers 300-300J illustrated in FIGS. 5A-11,for example, the blades 303 may be formed to have a curved profile witha radius of curvature, R. The radius of curvature R may be sized suchthat, when the impeller is in the stored or compressed configuration,the blades 303 conform closely to the hub 301. Indeed, in variousarrangements, the blades 303 in the stored configuration can have aradius R_(S) sized such that the blades 303 lie against the hub 301 in alow profile so that the insertion diameter of the catheter pump is smallenough to be safely inserted through the patient's vasculature. In someembodiments, the radius of curvature R and/or the height h of the blade303 are selected such that neighboring blades in a particular blade rowdo not overlap when the impeller is in the stored configuration. Byreducing or eliminating blade overlap in the stored configuration, theinsertion diameter of the catheter pump can be reduced. In otherarrangements, however, neighboring blades may overlap in the storedconfiguration.

Furthermore, when the impeller is urged out of an external sleeve, theimpeller can self-expand into a deployed configuration, in which theimpeller is deployed from the sleeve and expanded into a deployeddiameter larger than a stored diameter. In various embodiments, theself-expansion of the impeller can be induced by strain energy stored inthe blades 303, such as strain or potential energy stored near the rootof the blades 303. When the sleeve is urged away from the impeller, theblades 303 can be free to expand into the deployed configuration. Itshould be appreciated that when the blades 303 are in the deployedconfiguration, the blade(s) 303 can be in a relaxed state, such thatthere are no or minimal external forces (such as torque- or flow-inducedloads) and internal forces (such as strain energy stored in the blades)applied to the impeller or blades. A radius of curvature R_(D) of theblades 303 in the deployed configuration may be selected to improve flowcharacteristics of the pump while reducing the risk of hemolysis orother damage to the patient. For example, in some embodiments, theimpeller can be molded to form blades 303 having the desired deployedradius of curvature R_(D), such that in a relaxed (e.g., deployed)state, the blades 303 have a radius of curvature R_(D) that may beselected during manufacturing (e.g., molding). In some arrangements, theradius of curvature R_(D) of the blades in the deployed configurationmay be about the same as the radius of curvature R_(S) of the blades inthe stored configuration. In other arrangements, however, the radius ofcurvature of the blades 303 in the stored and deployed configurationsmay be different.

When the heart pump is activated to rotate the impeller, the impellerand blades 303 may be in an operational configuration. In theoperational configuration, the impeller may rotate to drive bloodthrough the housing 202. The rotation of the impeller and/or the flow ofblood past the impeller can cause the blades 303 to deform such that anoperational radius of curvature R_(o) may be induced when the impelleris in the operational configuration. For example, when the impellerrotates, the blades 303 may slightly elongate such that the free ends ofthe blades 303 extend further radially from the hub 301 relative to whenthe blades 303 are in the deployed configuration. As the blades 303deform radially outward in the operational configuration, theoperational radius of curvature R_(o) may therefore be larger than thedeployed radius of curvature R_(D). For example, in some embodiments, inthe operational configuration, the blades 303 may substantially flattensuch that there is little curvature of the blades during operation ofthe pump. Indeed, in the operational configuration, the blades 303 mayextend to an operational height h_(o) that is larger than the height hof the blades 303 when in the deployed configuration (see h asillustrated in the impellers 300-300J of FIG. 5A-11, which are in adeployed or relaxed configuration). In some embodiments, because theblades 303 may be manufactured to be relaxed when in the deployedconfiguration, the radius of curvature R_(D) and the height h of theblades 303 in the deployed configuration can be selected such that, inthe operational configuration, the blades 303 extend radially outwardfrom the hub 301 as far as possible without risking an overly small tipgap G (see FIG. 3C). Flow rate can be improved by enabling the blades303 to extend radially outward to a greater extent in the operationalconfiguration than in the deployed configuration.

It should be appreciated that the various parameters described hereinmay be selected to increase flow rate, even while reducing therotational speed of the impeller. For example, even at relatively lowimpeller rotational rates of 21,000 revolutions per minute (RPM) or less(e.g., rates in a range of about 18,000 RPM to about 20,000 RPM, or moreparticularly, in a range of about 18,500 RPM to about 19,500 RPM in somearrangements), the blades 303 can be designed to yield relatively highflow rates in a range of about 4 liters/minute (LPM) to about 5liters/minute. Conventional percutaneous rotary blood pumps have beenfound to deliver less than ideal flow rates even at rotational speeds inexcess of 40,000 RPM. It should be appreciated that higher impellerrotational rates may be undesirable in some aspects, because the highrate of rotation, e.g., higher RPMs, lead to higher shear rates thatgenerally increase hemolysis and lead to undesirable patient outcomes.By reducing the impeller rotational rate while maintaining or increasingflow rate, the pump in accordance with aspects of the invention canreduce the risk of hemolysis while significantly improving patientoutcomes over conventional designs.

Furthermore, to enable percutaneous insertion of the operative device ofthe pump into the patient's vascular system, the impellers 300-300Jdisclosed herein in FIGS. 5A-11 may also include a ramped surface at arearward or proximal end of the blade. As explained herein (see, e.g.,FIG. 12), when the external sleeve is urged against the housing 202(e.g., cannula), the external sleeve can press against the housing 202and the ramped surface of the impeller to collapse the impeller andblades into the stored configuration. For example, the ramped surfacecan be used to store the blades and impeller after assembly of the pumpfor packaging purposes and/or after performing a heart pumping procedurefor withdrawal of the pump from the anatomy.

The impellers disclosed herein may be formed of any suitable materialand by any suitable process. For example, in preferred embodiments, theimpeller is formed from a flexible material, e.g., an elastic materialsuch as a polymer. Any suitable polymer can be used. In someembodiments, for example, Hapflex 598, Hapflex 798, or Steralloy orThoralon may be used in various portions of the impeller body. In somearrangements, the impeller body can be molded to form a unitary body.

Various Impeller Designs

Turning to FIGS. 5A-5F, one embodiment of the impeller 300 is presented.It should be appreciated that FIGS. 5A-5F illustrate the same impeller300, only showing different views and impeller parameters for ease ofillustration. One or more blades 303 can extend from the hub 301, suchthat a fixed end of the blades 303 is integrally formed with or coupledto the hub 301. The blades 303 can also have a free end located at thetip of the blades 303. As used herein, therefore, it should beappreciated that the blades 303 can have a fixed end coupled to the hub301 (e.g., at a blade root) and a free end at a tip of the blade 303. Inthe illustrated embodiments, the hub 301 and blades 303 form a singleunitary, or monolithic, body. However, it should be appreciated that inother embodiments, the hub 301 and blades 303 may be formed fromseparate components or materials. In various implementations, theimpeller 300 can include one or more blade rows extending along the hub301.

FIGS. 5A-5F illustrate the impeller 300 having one blade row and twoblades 303. The hub 301 can have a first diameter D₁ at a distal endportion of the impeller 300 (e.g., near a leading edge of the blade(s)303) and a second diameter D₂ at a proximal end portion of the impeller300 (e.g., near a trailing edge of the blade(s) 303). As used herein andas shown in FIG. 5A, for example, a distal end portion of the impeller300 may be disposed nearer the distal end of the catheter pump, while aproximal end portion of the impeller 300 may be disposed nearer themotor and the insertion site. As explained below, in someimplementations, D₁ can be less than D₂. The hub 301 can also have alength L, and the blades 303 can have a height h, which can be thedistance between the hub and the free end of the blades. Further, eachblade 303 can have a blade length L_(b), which may or may not be thesame as the hub length L. As shown in FIG. 5A, the height h may bemeasured from the hub 301 to the free end of a middle portion of theblades 303 when the impeller is in a deployed or relaxed configuration.The height h may vary along the length of the blades 303, e.g.,increasing proximally from a forward or distal end of the blades 303 toa maximum in a middle portion of the blades and decreasing from themiddle portion to a rearward or proximal portion of the blades.Furthermore, as explained above, when the impeller 300 rotates and is inan operational configuration, the operational height h_(o) may be largerthan the blade height h in the deployed or relaxed configuration, whichis illustrated in FIGS. 5A-5F.

Furthermore, each blade 303 can include a suction side 305 and apressure side 307. In general, fluid can flow from the suction side 305of the blade 303 toward the pressure side 307 of the blade 303, e.g.,from the distal end portion of the impeller 300 to the proximal endportion of the impeller 300. The pressure side 307 can be include acurved, concave surface having a predetermined radius of curvature R, asbest seen in FIG. 5C, and as explained above. For example, in FIGS.5A-5F, the illustrated radius of curvature R corresponds to a relaxed ordeployed radius of curvature R_(D). As explained above, when theimpeller 300 rotates, the impeller may be in an operationalconfiguration having an operational radius of curvature R_(o) that maybe larger than the deployed radius of curvature R_(D). Indeed, in someembodiments, the blades 303 may substantially flatten and elongateradially such that there is little curvature. The elongated blades 303in the operational configuration may enable for increased flow ratethrough the pump.

Moreover, each blade 303 can have a thickness designed to improveimpeller performance. As shown in FIG. 5B, the leading edge or distalend portion of the blade 303 can have a first thickness t_(1a) at thefixed end of the blade 303, where the blade 303 joins the hub 301, and asecond thickness t_(1b) at the free end of the blade 303. Similarly, inFIG. 5C, the trailing edge of the blade 303 can also have a firstthickness t_(2a) at the fixed end of the blade 303 and a secondthickness t_(2b) at the free end of the blade 303. Example parametersfor various blades in FIGS. 5A-11 will be disclosed in the descriptionbelow and in Tables 1 and 2.

Each blade 303 can wrap around the hub 301 by a desired wrapping angle.The wrapping angle can be measured along the circumference of the hub301. As shown in the illustrated embodiments, each blade 303 canseparately track a helical pattern along the surface of the hub 301 asthe blade 303 wraps around the hub 301 along the length L of the hub.Table 2 and the disclosure below illustrate example wrapping angles forblades 303 in various embodiments. The blades can wrap around the hubany suitable number of turns or fractions thereof. Further, a firstfillet 311 can be formed at the fixed end of each blade on the suctionside 305, and a second fillet 313 can be formed at the fixed end of eachblade 303 on the pressure side 307. As shown each fillet 311, 313 canfollow the fixed end of each blade 303 as it wraps around the hub 301.As explained below, the first fillet 311 can be sized and shaped toprovide support to the blade 303 as the impeller 300 rotates. The secondfillet 313 can be sized and shaped to assist in folding or compressingthe blade 303 into the stored configuration.

In addition, each blade 303 can form various blade angles α, β, and γ.As shown in FIGS. 5D-F, the blade angles α (referred to herein as an“attack angle α” or a “distal blade angle α”), β (referred to herein asa “middle blade angle β”), and γ (referred to herein as a “proximalblade angle γ”) measure the angles between a blade centerline at variousportions of the blade and a plane that is perpendicular to the hub 301.For example, the attack angle α can measure the angle between a planeformed perpendicular to the blade near the distal portion of the blade(e.g., distally along the impeller hub in FIG. 5D) and a plane formedperpendicular to the hub 301. The attack angle α can range between about30 degrees and about 60 degrees. In some implementations, α can rangebetween about 40 degrees and about 55 degrees. In the implementation ofFIG. 5D, for example, α can be in a range of about 48 degrees and about52 degrees, e.g., about 50 degrees. The middle blade angle β can measurethe angle between a plane perpendicular to the blade in a middle portionof the blade and a plane perpendicular to the hub 301. In someimplementations, β can range from about 30 degrees to about 45 degrees.In the implementations of FIGS. 5A-5F and 6, for example, β can be in arange of about 35 degrees and about 42 degrees, e.g., about 40 degrees.The proximal blade angle γ can correspond to the angle between a planeperpendicular to the blade in a proximal portion of the blade (e.g.,proximal with respect to the hub 301) and a plane perpendicular to thehub 301. In some embodiments, γ can range between about 25 degrees andabout 55 degrees. In the illustrated embodiment of FIG. 5F, γ can be ina range of about 30 degrees and about 40 degrees, or about 35 degrees,for example. In some embodiments, the attack angle α can be larger thanthe middle blade angle β. Further, in some embodiments, the middle bladeangle can be larger than the proximal blade angle γ. In someembodiments, the attack angle α can be larger than both the middle bladeangle β and the proximal blade angle γ. The blade angles α, β, and γ canbe further designed using computational techniques to maintain desiredflow characteristics, such as flow rate, pressure head, and rotationalspeed. For example, the disclosed blade angles can, in various impellersdisclosed herein, enable flow rates in a range of about 4 liters/minuteto about 5.5 liters/minute, when the impeller rotates at a speed belowabout 20,000 RPMs (e.g., in a range of about 19,000 RPMs to about 21,000RPMs in some arrangements). By maintaining a high flow rate atrelatively low rotational speeds, the disclosed impellers can achievedesirable patient outcomes while reducing the risk of hemolysis andincreasing pump reliability.

Further, the trailing edge of each blade 303 can include a ramp 315forming a ramp angle θ with the plane perpendicular to the hub 301, asbest illustrated in FIG. 5C. The ramp 315 can be shaped such that whenthe sheath and housing 202 are urged against the ramp 315, or when theblades 303 and housing 202 are pulled proximally relative to and intothe sheath, the axial force applied by the sheath can be transferreddownward by the ramp 315 to assist in folding the blade 303 against thehub 301. The ramp angle θ can be configured to assist in folding theblade 303 against the hub 301. Further, the cross-sectional curvatureand/or axial form of the blades can also be configured to reduce theforce needed to collapse the impeller when used in conjunction with theramp angle θ. For example, the angle that the blades twist around thehub may be configured to direct axial forces applied by the sheath tofold the blades against the hub 301. The radius of curvature R of theblades 303 can also be selected to enable the blades 303 to conformclosely to the hub 301, as explained above.

Turning to FIGS. 6-11, other embodiments of the impeller 300 areillustrated. Reference numerals in FIGS. 6-11 generally representcomponents similar to those of FIGS. 5A-5F. In addition, it should beappreciated that the parameters and angles described above withreference to FIGS. 5A-5F are also present in the impellers disclosed inFIGS. 6-11, even where such parameters or angles are not specificallyreferenced for ease of illustration. For example, FIG. 6 illustrates animpeller 300A having two blades 303 in one blade row. On the other hand,FIG. 7 illustrates an impeller 300B having three blades 303 in a singleblade row. FIG. 8 illustrates another example of an impeller 300C havingtwo blades 303 in one blade row. FIGS. 9A-9C illustrate three impellers300F-300H, respectively, each having two blades in one row. FIG. 9Dillustrates an impeller 3001 having three blades in one row. Bycontrast, FIG. 9E shows an impeller 300J having four blades total, withtwo blade rows, each blade row having two blades. FIGS. 10A-10Billustrate yet another impeller 300D having three blades 303 in a singlerow, while FIG. 11 shows an impeller 300E having two blades 303 in asingle row. Tables 1 and 2 include various properties for the impellers300 shown in the embodiments of FIGS. 5A-5C and 6-11. The impellers300-300J disclosed herein may have different values for the variousparameters and characteristics disclosed herein, and some of theimpellers may have improved performance relative to other of thedisclosed impellers.

The impellers 300 illustrated in the disclosed embodiments may haveother features. For example, for impellers with multiple blade rows, theblade(s) in one row may be angularly clocked relative to the blade(s) inanother row. It should be appreciated that the blades may be configuredin any suitable shape or may be wrapped around the impeller hub in anymanner suitable for operation in a catheter pump system.

Impeller Parameters

As explained above, various impeller parameters can be important inincreasing flow rate while ensuring that the pump operates safely withinthe subject. Further, various properties and parameters of the disclosedimpellers 300-300J of FIGS. 5A-11 may enable the impellers to moreeasily collapse into the stored configuration.

Hub Diameter and Length

One impeller parameter is the size of the hub, e.g., the diameter and/orthe length of the hub. As illustrated in FIGS. 5A-11, the hub can betapered in various embodiments, such that the distal end portion of thehub has a first diameter, D₁, and the proximal end portion of the hubhas a second diameter, D₂. The first and second diameters, D₁ and D₂ candetermine the spacing between the wall W of the housing 202 and the hub301. Since the housing 202 effectively bounds the area through whichblood can flow, the spacing between the hub 301 and the housing wall Wmay determine the maximum flow rate through the pump. For example, ifthe hub 301 has a relatively small diameter, then the flow area betweenthe inner wall W of the housing 202 and the hub 301 may be larger thanin embodiments with a larger hub diameter. Because the flow area islarger, depending on other impeller parameters, the flow rate throughthe pump may advantageously be increased.

One of skill in the art will appreciate from the disclosure herein thatthe impeller parameters may be varied in accordance with the invention.The hub diameter can vary. In some embodiments, D₁ can range betweenabout 0.06 inches and about 0.11 inches. D₂ can range between about 0.1inches and about 0.15 inches. For example, in the impeller shown inFIGS. 5A-5F, D₁ can be about 0.081 inches, and D₂ can be about 0.125inches. In the implementation of FIGS. 10A and 10B, D₁ can be in a rangeof about 0.08 inches and about 0.09 inches (e.g., about 0.0836 inches insome arrangements), and D₂ can be in a range of about 0.12 inches andabout 0.13 inches (e.g., about 0.125 inches in some arrangements).

Moreover, the length, L_(b), of each blade can be designed in variousembodiments to achieve a desired flow rate and pressure head. Ingeneral, longer blades can have higher flow rates and pressure heads.Without being limited by theory, it is believed that longer blades cansupport more blade material and surface area to propel the blood throughthe cannula. Thus, both the length of the blades and the first andsecond diameters D₁ and D₂ can be varied to achieve optimal flow rates.For example, D₁ can be made relatively small while L_(b) can be maderelatively long to increase flow rate.

Blade Height

Another impeller parameter is the height h of the blades of the impellerin the deployed, or relaxed, configuration. The height h of the bladescan be varied to achieve a stable flow field and to reduce turbulence,while ensuring adequate flow rate. For example, in some embodiments, theblade can be formed to have a height h large enough to induce adequateflow through the cannula. However, because the blades are preferablyflexible so that they can fold against the hub in the storedconfiguration, rotation of the impeller may also cause the blades toflex radially outward due to centrifugal forces. As explained above withrespect to FIGS. 3A-3C, the tip gap G between the wall W of the housing202 and the free ends of the blades can be quite small. If the blades303 flex outwardly by a substantial amount when the impeller 300rotates, then the distal ends of the blades 303 may impact the housingwall W, which can damage blood cells passing by. Thus, the height h mayalso be formed to be sufficiently small such that, upon rotation of theimpeller 300, deformation of the blades 300 still maintains adequate tipgap G.

On the other hand, as explained above, the height h of the blades 303 inthe deployed configuration can be selected such that when the impellerrotates, the tip or free end of the blades 303 can extend or elongate toan operational height h_(o), which extends further radially than when inthe deployed configuration, in order to increase flow rate. Thus, asexplained herein, the height h and the radius of curvature R_(D) of theblades 303 in the deployed configuration can be selected to bothincrease flow rate while reducing the risk of hemolysis caused byinadequate tip gap G.

In various implementations, the height of the blades near the middle ofthe impeller hub can range between about 0.06 inches and about 0.15inches, for example, in a range of about 0.09 inches to about 0.11inches. Of course, the height of the blades can be designed inconjunction with the design of the hub diameters and length, and withthe radius of curvature R. As an example, for the impeller in FIGS.5A-5C, the height h of the blade near the middle of the impeller hub canbe in a range of about 0.09 inches and about 0.1 inches (e.g., about0.0995 inches in some arrangements). In the impeller of FIGS. 10A-10B,the height h of the blade can be in a range of about 0.1 inches andabout 0.11 inches (e.g., about 0.107 inches in some arrangements). Otherexample blade heights may be seen in Table 1.

Number of Blades

As mentioned above, impellers 300 can have any suitable number of blades303. In general, in impellers with more blades 303, the flow rate ofblood flowing through the cannula or housing 202 can be advantageouslyincreased while reducing the required angular velocity of the driveshaft. Thus, absent other constraints, it can be advantageous to use asmany blades as possible to maximize flow rate. However, because theimpellers disclosed herein can be configured to fold against the hub 301in the stored configuration for insertion into a patient's vasculature,using too many blades 303 can increase the overall volume of theimpeller in the stored configuration. If the thickness of the impeller300 in the stored configuration exceeds the diameter of the sheath orsleeve (or the diameter of the patient's artery or vein), then theimpeller 300 may not collapse into the sheath for storing.

Moreover, increasing the number of blades 303 accordingly increases thenumber of shear regions at the free end of the blades 303. As theimpeller 300 rotates, the free ends of the blades 303 induce shearstresses on the blood passing by the blades 303. In particular, the tipor free edge of the blades 303 can induce significant shear stresses. Byincreasing the overall number of blades 303, the number of regions withhigh shear stresses are accordingly increased, which candisadvantageously cause an increased risk of hemolysis in somesituations. Thus, the number of blades can be selected such that thereis adequate flow through the pump, while ensuring that the impeller 300can still be stored within the sheath and that the blades 303 do notinduce excessive shear stresses. In various arrangements, for example,an impeller having three blades (such as the impellers shown in FIGS. 7,9D, and 10A-10B) can achieve an appropriate balance between increasedflow rate and reduced risk of hemolysis.

Radius of Curvature

Yet another design parameter for the impeller is the radius ofcurvature, R, of the blades 303 on the pressure side 307 of the blades,as explained in detail above. As shown in FIGS. 5A-11, the illustratedimpellers 300-300J are in the deployed configuration, such that theillustrated R corresponds to the deployed radius of curvature R_(D). Theradius of curvature R can be designed to minimize turbulence, whileincreasing flow rate. Turbulence can disadvantageously dissipate energyas the impeller rotates, which can reduce the flow rate. In general,higher curvature on the pressure side 307 of the blades 303 can increaseturbulence. Moreover, the radius of curvature R can be designed toconform to the hub 301 such that, when the impeller is compressed by thesheath or sleeve, the curved pressure side 307 of the blade 303 conformsto the curvature of the hub 301 when the blades 303 are folded againstthe hub. Thus, the radius of curvature R of the blades can be designedto both reduce turbulent flow and to assist in folding the bladesagainst the hub to ensure that the impeller 300 fits within the sheathin the stored configuration.

In addition, as explained above, when the impeller rotates and is in theoperational configuration, the free end of the blades 303 may extendradially outward such that the radius of curvature in the operationalconfiguration, R₀, may be higher than the radius of curvature in theoperational configuration, R_(D), which is illustrated as R in FIGS.5A-11. Indeed, the straightening and elongation of the blades 303 in theoperational configuration may advantageously increase flow rate throughthe pump system.

The radius of curvature can range between about 0.06 inches and about0.155 inches in various embodiments. In some embodiments, the radius ofcurvature can range between about 0.09 inches and about 0.14 inches. Forexample, in the implementation of FIGS. 5A-5C, the cross-sectionalradius of curvature R at the leading edge of the blades can be in arange of about 0.11 inches and about 0.13 inches (e.g., about 0.12inches in some arrangements). By comparison, the radius of curvature Rof the leading edge of the blades in the impeller 300 shown in FIGS.10A-10B (in the deployed configuration) can be in a range of about 0.13inches to about 0.14 inches (e.g., about 0.133 inches in somearrangements). Other curvatures may be suitable in various embodiments.Table 2 illustrates example values for the radius of curvature R ofvarious embodiments disclosed herein, when the impellers are in thedeployed configuration.

Blade Thickness

In addition, the thickness of the blades 303 can be controlled invarious implementations. In general, the thickness of the blades canrange between about 0.005 inches and about 0.070 inches in someembodiments, for example in a range of about 0.01 inches to about 0.03inches. It should be appreciated that the thickness can be any suitablethickness. The thickness of the blade 303 can affect how the blade 303collapses against the hub 301 when compressed into the storedconfiguration and how the blade deforms when rotating in an operationalconfiguration. For example, thin blades can deform more easily thanthicker blades. Deformable blades can be advantageous when they elongateor deform by a suitable amount to increase flow rate, as explainedabove. However, as explained above, if the blade 303 deforms outward byan excessive amount, then the free end of the blade candisadvantageously contact the inner wall of the housing 202 when theimpeller 300 rotates. On the other hand, it can be easier to fold thinblades against the hub 301 because a smaller force can sufficientlycompress the blades 303. Thus, it can be important in some arrangementsto design a blade sufficiently stiff such that the blade 303 does notoutwardly deform into the cannula or housing 202, while still ensuringthat the blade 303 is sufficiently flexible such that it can be easilycompressed into the stored configuration and such that it deforms enoughto achieve desired flow rates.

In some embodiments, the thickness of each blade can vary along theheight h of the blade. For example, the blades can be thinner at theroot of the blade 303, e.g., near the hub 301, and thicker at the freeend of the blade 303, e.g., near the wall W of the cannula housing 202.As best seen in FIGS. 5B-5C, for example, the leading edge of the bladecan have a first thickness t_(1a) at the fixed end of the blade 303 anda second thickness t_(1b) at the free end of the blade 303. Moreover,the trailing edge of the blade 303 can have a first thickness t_(2a) atthe fixed end of the blade 303 and a second thickness t_(2b) at the freeend of the blade 303. Because the blades 303 are relatively thin nearthe hub 301, the blades 303 can be easily folded into the storedconfiguration due to their increased flexibility near the hub 301.Because the blades 303 are relatively thick at the free end (e.g., nearthe cannula wall W), the blades 303 may deform a suitable amount whenthe impeller rotates, reducing the risk that the blades 303 will contactor impact the wall W, which can accordingly reduce the risk ofhemolysis, while deforming enough to achieve desirable flow rates.Moreover, in some embodiments, the thickness may vary continuously, suchthat there are no steps or discontinuities in the thickness of theblade. For example, even though the free end of the blades may bethicker in some embodiments, the thickness can continuously increasealong the height of the blade.

As an example, the first thickness t_(1a) of the leading edge of theblade in FIGS. 5A-5C can be in a range of about 0.016 inches to about0.023 inches near the hub (e.g., about 0.02 inches at the hub in somearrangements), while the second thickness t_(1b) can be in a range ofabout 0.022 inches to about 0.028 inches at the free end (e.g., about0.025 inches at the free end in some arrangements). Further, at thetrailing edge of the blade of FIGS. 5A-5C, the first thickness t_(2a)can be in a range of about 0.016 inches to about 0.023 inches near thehub (e.g., about 0.02 inches at the hub in some arrangements), and thesecond thickness t_(2b) can be in a range of about 0.03 inches to about0.04 inches at the free end (e.g., about 0.035 inches at the free end insome arrangements). As another example, for the blade of FIGS. 10A-10B,the first thickness t_(1a) of the leading edge can be in a range ofabout 0.022 inches to about 0.028 inches at the hub (e.g., about 0.025inches near the hub in some arrangements), and the second thicknesst_(1b) can be in a range of about 0.022 inches to about 0.028 inches atthe free end (e.g., about 0.025 inches at the free end in somearrangements). At the trailing edge of the blade of FIGS. 10A-10B, thefirst thickness t_(2a) can be in a range of about 0.016 inches to about0.023 inches at the hub (e.g., about 0.02 inches in some arrangements),and the second thickness t_(2b) can be in a range of about 0.016 inchesto about 0.023 inches at the free end (e.g., about 0.02 inches in somearrangements).

Fillets at Root of Blades

As explained above, a first fillet 311 can extend along the suction side305 of each blade 303 at the proximal end of the blade 303 (e.g., at theroot of the blade), and a second fillet 313 can extend along thepressure side 307 of each blade at the proximal end of the blade 303. Ingeneral the first fillet 311 can have a larger radius than the secondfillet 313. The larger fillet 311 can be configured to apply a restoringforce when the impeller 300 rotates in the operational configuration. Asthe impeller 300 rotates, the blades 303 may tend to deform in thedistal direction in some situations (e.g., toward the distal portion ofthe hub 301). By forming the fillet 311 at the suction side 305 of theblade, the curvature of the fillet can advantageously apply a restoringforce to reduce the amount of deformation and to support the blade.

By contrast, the second fillet 313 formed on the pressure side 307 ofthe blade 303 can have a smaller radius than the first fillet 311. Thesecond fillet 313 can be configured to enhance the folding of the bladeagainst the impeller when the blades 303 are urged into the storedconfiguration.

The radius r of each fillet can be any suitable value. For example, theradius r₁ of the first fillet 311 can range between about 0.006 inchesand about 0.035 inches. The radius r₂ of the second fillet 313 can rangebetween about 0.001 inches and about 0.010 inches. Other fillet radiusesmay be suitable. For the implementation of FIGS. 5A-5C, for example, theradius r₁ of the first fillet 311 can be about 0.015 inches, and theradius r₂ of the second fillet 313 can be about 0.005 inches. Bycontrast, for the impeller shown in FIGS. 10A-10B, the first fillet 311can have a radius r₁ of about 0.025 inches, and the second fillet 313can have a radius r₂ of about 0.005 inches.

Wrapping Angle

In some implementations, the wrapping angle of each blade can bedesigned to improve pump performance and to enhance folding of theimpeller into the stored configuration. In general, the blades can wraparound the hub at any suitable angle. It has been found that wrappingangles of between about 150 degrees and about 220 degrees can besuitable for folding the blades into the stored configuration. Further,wrapping angles of between about 180 degrees and about 200 degrees canbe particularly suitable for folding the blades into the storedconfiguration.

Ramping Surface

Furthermore, as explained above, the trailing edge or the proximal endof each blade can include a ramp or chamfer formed at an angle θ with aplane perpendicular to the hub 301, as illustrated above in, e.g., FIG.5C. FIG. 12 is a schematic, side cross-sectional view of an impeller1200 having a hub 1201 and one or more blades 1203 disposed within ahousing 1202, similar to the housing 202 described above. As shown inFIG. 12, the impeller 1200 is in the expanded or deployed configuration.For example, the impeller 1200 may be in the deployed configurationbefore packaging and shipping to a customer. Alternatively, the impeller1200 may be in the deployed configuration after pumping blood in apatient and before withdrawal of the pump from the vasculature. Asexplained above, it can be desirable to compress the impeller 1200 intothe stored configuration for inserting or withdrawing the operativedevice of the pump from the patient. To assist in compressing theimpeller 1200 into the stored configuration, the blade(s) 1203 caninclude a ramp 1215 forming a ramp angle θ with a plane perpendicular tothe hub 1201.

An outer sheath or sleeve 1275 can be provided around an elongate bodythat extends between an operative device of the pump and the motor inthe system. The sleeve 1275 can be used to deploy the impeller 1200 fromthe stored configuration to the deployed configuration and to compressthe impeller 1200 from the deployed configuration back into the storedconfiguration. When compressing and storing the impeller 1200 and thehousing 1202, for example, a user, such as a clinician, can advance thesleeve 1275 in the +x-direction, as shown in FIG. 12. When urged in the+x-direction, the sleeve 1275 can bear against a contact portion 1235 ofthe housing 1202. The contact portion 1235 of the housing 1202 can inturn bear against the ramp 1215. Advantageously, the ramp angle θ can beangled distally such that when the sheath or sleeve 1275 is urged overthe impeller 1200 and housing 1202, the contact portion 1235 can contactthe angled or ramped edge of the blades to compress the blades againstthe hub. The ramp angle θ can be any suitable angle. For example, insome embodiments, the ramp angle θ can be between about 30 degrees andabout 50 degrees. In the implementation of FIGS. 5A-5C and 12, forexample, the chamfer or ramp angle θ of the ramp 1215 can be in a rangeof about 40 degrees to 50 degrees (e.g., about 45 degrees in somearrangements). In the embodiment of FIGS. 10A-10B, the ramp angle θ ofthe trailing edge can be in a range of about 35 degrees to 45 degrees(e.g., about 40 degrees in some arrangements). Still other ramp angles θmay be suitable to assist in storing the impeller. In some embodiment,the ramp 1215 can comprise a solid, relatively stiff portion againstwhich the housing 202 and sheath may be advanced.

Improving Patient Outcomes

As explained herein, it can be desirable to pump blood at relativelyhigh flow rates in order to provide adequate cardiac assistance to thepatient and to improve patient outcomes. It should be appreciated that,typically, higher impeller rotational speeds may increase flow ratesbecause the impeller is driven at a higher speed. However, one potentialdisadvantage of high impeller speeds is that blood passing across orover the rotating components (e.g., the impeller and/or impeller shaftor hub) may be damaged by the shearing forces imparted by the relativelyrotating components. Accordingly, it is generally desirable to increaseflow rates for given rotational impeller speeds.

The various features disclosed herein can enable a skilled artisan toprovide an impeller capable of increasing or maintaining flow rates atlower rotational impeller speeds. These improvements are not realized bymere increases in rotational speed or optimization of the impellerdesign. Rather, the improvements lead to a significant shift in theperformance factor of the impeller, which reflect structural advantagesof the disclosed impellers.

FIG. 13 is a chart plotting flow rate versus motor speed for theimpellers illustrated in FIGS. 10A-10B and 9E. Note that, in theillustrated chart of FIG. 13, however, that the impeller speed is thesame as the motor speed, e.g., no clutch is used between the motor andimpeller shaft. Thus, the plotted values in FIG. 13 represent flow ratesat various impeller rotational speeds. The flow rates were measured byrunning the impellers on a closed mock loop on the bench with a bloodanalog. The back pressure (e.g., head pressure or change in pressureacross the pump) was at about 62 mmHg for the impellers 300D, 300J ofFIGS. 10A-10B and 9E, respectively. The results on the bench top mirrorthose achieved in animal investigations.

As shown in FIG. 13, the impeller 300D provides for higher flow rates atlower speeds than the impeller 300J of, e.g., FIG. 9E. For example, theimpeller 300J of FIG. 9E may be capable of pumping blood at flow ratesin a range of about 4.5 liters per minute (LPM) to about 5.5 LPM whenthe impeller is operating at speeds in a range of about 25,000revolutions per minute (RPMs) to about 28,000 RPMs. For example, theimpeller of FIG. 9E may be capable of pumping blood at a flow rate ofabout 5.5 LPM when the impeller is operating at speeds in a range ofabout 26,000 RPMs to about 28,000 RPMs.

In FIG. 13, the flow rate of the impeller 300J can be plotted along aline X, in which flow rate increases with impeller rotational speed,which is the same as motor speed in FIG. 13. With prior designs,increased flow rate can only be achieved by increasing the rotationalspeed to move along the line X Prior, it was expected that optimizationof the impeller design can only realize minor improvements to the flowversus RPM curve. At best, the impeller could be configured to achieveminor improvements at the extremes or with a slight change in the curveX, such that the line or curve X might have a slightly higher slope.

For example, with the impeller 300J of FIG. 9E, the impeller speed atdata point X1 is about 21,000 RPM, which yields a flow rate of about 1.9LPM. With the impeller 300J of FIG. 9E, flow rate can indeed beincreased to above about 5 LPM, e.g., about 5.4 LPM, at data point X2,but the impeller rotational speed required to achieve such improvementsin flow rate also increases to about 27,000 RPM. Thus, even though theimpeller 300J of FIG. 9E can achieve relatively high flow rates, thehigh flow rates come at the expense of a higher impeller speed, which,as explained above, can cause hemolysis and undesirable patientoutcomes.

By contrast, the impeller 300D of FIGS. 10A-10B achieves significant andunexpected performance improvements. The exemplary impeller has beenfound to achieve dramatically higher flow rates at all rotationalspeeds. For example, the impeller 300D of FIGS. 10A-10B can achieve flowrates above 4.25 LPM, indeed even above about 5 LPM, while maintaining alow impeller speed of less than about 21,000 RPM (which, by contrast,induced a flow rate of only about 1.9 LPM in the impeller 300J of FIG.9E). Thus, the design of the impeller 300D of FIGS. 10A-10B canadvantageously achieve structural advantages relative to the impeller300J. Indeed, the curve labeled Yin FIG. 13 illustrates the dramaticshift of the flow rate curve to the left in FIG. 13, which indicatessignificantly increased flow rates at lower impeller speeds relative toprior impeller designs. The exemplary impeller has also been found tohave a dramatically improved head pressure versus flow rate (HQ)performance versus conventional designs.

The exemplary impeller 300D of FIGS. 10A-10B has been found to becapable of pumping blood at flow rates in a range of about 4.5 LPM toabout 5.5 LPM when the impeller is operating at speeds in a range ofabout 19,000 RPM to about 21,000 RPM, e.g., when the impeller isoperating at speeds less than about 21,000 RPMs. For instance, theimpeller 300D of FIGS. 10A-10B may be capable of pumping blood at a flowrate of about 5.5 LPM when the impeller is operating at speeds in arange of about 20,000 RPMs to about 21,000 RPMs. Further, the impeller300D of FIGS. 10A-10B may be capable of pumping blood at a flow rate ofabout 5 LPM when the impeller is rotating at speeds in a range of about19,000 RPMs to about 21,000 RPMs. In some arrangements, when theimpeller is operating at a speed of about 19,500 RPMs, the flow rate maybe in a range of about 4.5 LPM to about 5.1 LPM.

Further, the impeller 300D of FIGS. 10A-10B is capable of pumping bloodat a flow rate of at least about 3.5 LPM, and/or at least about 4.25LPM, when the impeller is operating at speeds less than about 21,000RPMs. For example, the impeller 300D is capable of pumping blood at aflow rate of at least 4.25 LPM when the impeller is operating at speedsin a range of about 18,500 RPM to about 22,000 RPM, for example in arange of about 18,500 RPM to about 21,000 RPM. For example, the impeller300D is capable of pumping blood at a flow rate in a range of about 4.25LPM to about 5.5 LPM when the impeller is operating at speeds in a rangeof about 18,500 RPM to about 21,000 RPM. The flow rates achieved atthese impeller speeds may be achieved at a back pressure or headpressure of at least 60 mmHg, e.g., at about 62 mmHg in someembodiments. Further the impeller 300D capable of achieving theperformance of FIG. 13 may also be sized and shaped to be inserted intoa vascular system of a patient through a percutaneous access site havinga catheter size less than about 21 FR.

The impeller 300D of FIGS. 10A-10B may therefore provide a dramatic andunexpected jump in flow rates relative to the impeller 300J of FIG. 9E.The shift in performance allows the impeller 300D to achieve a maximumflow rate far exceeding conventional and/or previous designs and at arotational speed a mere fraction of that for which conventional pumpsare designs. Thus, FIG. 13 illustrates that the impeller 300D of FIGS.10A-10B yields improved patient outcomes and reduced hemolysis relativeto the impeller 300J of FIG. 9E.

FIG. 14 is a chart plotting flow rate versus motor speed (e.g., impellerspeed) for an impeller similar to or the same as the impeller 300D ofFIGS. 10A-10B, as compared to various conventional microaxial, rotarypumps. In particular, Curve A in FIG. 14 plots flow rate versus motorspeed (again, the same as impeller speed in FIG. 14) for the impellerassociated with Curve A, according to test data taken using a bloodanalog at about 62 mmHG back pressure.

Curve B plots approximate flow rate versus motor speed for the heartpump disclosed in the article of J. Stolinski, C. Rosenbaum, WillemFlameng, and Bart Meyns, “The heart-pump interaction: effects of amicroaxial blood pump,” International Journal of Artificial Organs, vol:25 issue: 11 pages: 1082-8, 2002, which is incorporated by referenceherein in its entirety and for all purposes. The test data from Curve Bwas obtained under test conditions having a back pressure of about 60mmHg.

Curve C plots approximate flow rate versus motor speed for the heartpump disclosed in the article of David M. Weber, Daniel H. Raess, JoseP. S. Henriques, and Thorsten Siess, “Principles of Impella CardiacSupport,” Supplement to Cardiac Interventions Today, August/September2009, which is incorporated by reference herein in its entirety and forall purposes. The test data from Curve C was obtained under testconditions having a back pressure of about 60 mmHg.

Data point D plots approximate flow rate versus motor speed for theheart pump disclosed in Federal and Drug Administration 510(k) Summaryfor Predicate Device IMPELLA 2.5 (K112892), prepared on Sep. 5, 2012,which is incorporated by reference herein in its entirety and for allpurposes. In particular, for data point D, the disclosed pump wascapable of mean flow rates of up to 3.3 LPM at pump speeds of 46,000 RPMat a 60 mmHg differential pressure.

As shown in FIG. 14, the disclosed impeller associated with Curve A canachieve higher flow rate at all impeller speeds relative to the pumps ofCurves B, C, and D. The data reflected in FIG. 14 was not all collectedby precisely the same methodology in a head-to-head fashion, as notedabove. However, the data are shown on a single chart for the convenienceof the reader and are still compelling. For example, as discussed above,the back-pressure conditions under which the Curve A data was collected(for impellers disclosed herein) was higher than that collected for theother devices. Were this test condition the same, the results would beall the more impressive. Indeed, data points A1 and A2 of Curve A, forexample, provide higher flow rates at significantly lower impellerrotation rates than any of the data points along Curves B-C or at pointD (e.g., data points B1, B2, B3, C1, C2). In addition, as shown in FIG.14, the impeller of Curve A can achieve flow rates of about 7 LPM atimpeller speeds of only about 25,000 RPM, as shown by Curve A. Bycontrast, curves B-C and data point D do not even indicate that theconventional axial pumps can achieve 7 LPM flow rates at any impellerspeed. Thus, the impeller associated with Curve A of FIG. 14 can achievehigher flow rates at lower rotational speeds than conventional catheterpumps, such as microaxial, rotary pumps, (e.g., Curves B-C and datapoint D of FIG. 14). In addition, the disclosed impellers can also beconfigured to achieve higher maximum flow rates than conventional pumps.

In addition, the data of Curves B-C and data point D of FIG. 14represent another constraint on the design of conventional rotary pumps.For example, the pump plotted on Curve B has a diameter corresponding toa catheter size of about 21 FR. Flow rates may be increased for the pumpof Curve B by increasing the diameter of the pump. However, furtherincreases in pump diameter for the device of Curve B maydisadvantageously increase the pump diameter requiring more invasivetechniques to position the pump. Thus, increasing flow rate byincreasing pump diameter may not be a feasible or desirable alternativefor catheter pumps, and/or it may not be desirable for acute heartfailure where fast implantation is critically important.

By contrast, as shown in Curve A of FIG. 14, the impeller (e.g., whichcan be the same as or similar to the impeller 300D disclosed herein)advantageously has an insertion diameter corresponding to a cathetersize of less than about 13 FR, e.g., about 12.5 FR in some embodiments,which can enable minimally-invasive insertion techniques, even at higherflow rates and lower impeller rotation rates. Thus, the disclosedimpeller of Curve A can provide higher flow rates at lower impellerspeeds than conventional microaxial, rotary pumps, and can maintainlower insertion diameters for minimally invasive techniques.

Indeed, the impeller of Curve A may be configured to be inserted intovascular system of a patient through a percutaneous access site having asize less than 21 FR. The impeller of Curve A (e.g., which may besimilar to or the same as impeller 300D) may include one or more bladesin a single row. In some embodiments, the impeller can be configured topump blood through at least a portion of the vascular system at a flowrate of at least about 2.0 liters per minute when the impeller isrotated at a speed less than about 21,000 revolutions per minute. Insome embodiments, the blades are expandable.

Blade Height-to-Hub Diameter Ratio

In some embodiments, a ratio σ of blade height (h) to hub diameter (D)can be defined. As explained above, the hub 301 can have a firstdiameter D₁ at a distal end portion of the impeller 300 (e.g., near aleading edge of the blade(s) 303) and a second diameter D₂ at a proximalend portion of the impeller 300 (e.g., near a trailing edge of theblade(s) 303). As used herein, the ratio σ may be defined relative to adiameter D, which, in some embodiments, may correspond to the firstdiameter D₁ or the second diameter D₂, or to an average of D₁ and D₂.The blade height h may be identified relative to the deployedconfiguration in some embodiments. As shown in FIGS. 5A-11, the height hmay be defined by a maximum distance between the hub 301 and the freeend of the blade(s) 303.

The ratio σ may be relatively large compared to conventional impellers.For example, as explained herein, it can be advantageous to provide foran impeller 300 having a low profile suitable, for example, forpercutaneous insertion into the patient's vascular system. One way toprovide a low profile impeller 300 is to reduce the volume of impellermaterial that is compressed within the outer sheath, e.g., the sheathwithin which the impeller 300 is stored during percutaneous delivery andinsertion. Impellers having relatively large blade height-to-hubdiameter ratios σ may allow for such compact insertion, whilemaintaining high flow rates. For example, larger blade heights h canallow for the use of smaller hub diameters D, and the larger bladeheights h are also capable of inducing high flow rates that areadvantageous for catheter pump systems. For example, in someembodiments, the blade height-to-hub diameter ratio σ can be at leastabout 0.95, at least about 1, at least about 1.1, and/or at least about1.2, in various arrangements. In some embodiments, for example, theratio σ can be in a range of about 0.7 to about 1.45 in variousembodiments. In particular, the ratio σ can be in a range of about 0.7to about 1.1 in some embodiments (such as the embodiment of FIGS.10A-10B, for example). In addition, in some arrangements, the ratio σcan be in a range of about 0.75 to about 1. In some embodiments, theratio σ can be in a range of about 0.9 to about 1.1.

Example Impeller Parameters

It should be appreciated that the values for the disclosed impellerparameters are illustrative only. Skilled artisans will appreciate thatthe blade parameters can vary according to the particular designsituation. However, in particular embodiments, the blade parameters caninclude parameter values similar to those disclosed in Tables 1-2 below.Note that length dimensions are in inches and angles are in degrees.

TABLE 1 FIG. No. of D₁ D₂ h t_(1a) t_(1b) t_(2a) t_(2b) Number Blades(in.) (in.) (in.) (in.) (in.) (in.) (in.) 5A-5F  2 0.081 0.125 0.09950.02 0.025 0.02 0.035 6 2 0.081 0.125 0.1 0.02 0.02 0.015 0.02 7 30.0844 0.125 0.1025 0.015 0.015 0.02 0.02 8 2 0.097 0.12 0.107 0.0150.02 0.015 0.02 10A-10B 3 0.0836 0.125 0.107 0.025 0.025 0.02 0.02 11  20.0798 0.125 0.109 0.03 0.025 0.015 0.02

TABLE 2 FIG. β Wrap Angle θ r₁ r₂ R Number (deg) (deg) (deg) (in.) (in.)(in.) 5A-5F  40 210 45 0.015 0.005 0.12 6 40 210 45 0.015 0.005 0.07 740 270 46 0.015 0.005 0.133 8 40 200 40 0.015 0.005 0.12 10A-10B 40 22040 0.025 0.005 0.133 11  30 210 35 0.015 0.005 0.09

One will appreciate from the description herein that the configurationof the blades may be modified depending on the application. For example,the angle of attack of the blades may be modified to provide for mixedflow, axial flow, or a combination thereof. The exemplary blades of theillustrated figures are dimensioned and configured to improve axial flowand reduce hemolysis risk. The exemplary blades are shaped anddimensioned to achieve the desired pressure head and flow rate. Inaddition, the single blade row design is thought to reduce the turbulentflow between blade rows with other designs and thus may reducehemolysis.

Although the inventions herein have been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent inventions. It is therefore to be understood that numerousmodifications can be made to the illustrative embodiments and that otherarrangements can be devised without departing from the spirit and scopeof the present inventions as defined by the appended claims. Thus, it isintended that the present application cover the modifications andvariations of these embodiments and their equivalents.

What is claimed is:
 1. An impeller for a catheter pump, the impellercomprising: a hub having a proximal end portion and a distal endportion; and at least one blade supported by the hub, the at least oneblade transitionable between a stored position and a deployed position,the at least one blade having a fixed end coupled to the hub and a freeend, wherein the at least one blade comprises: a distal blade angledefined between a plane perpendicular to the free end of the blade neara distal end of the blade and a plane perpendicular to the hub; aproximal blade angle defined between a plane perpendicular to the freeend of the blade near a proximal end of the blade and a planeperpendicular to the hub; and a middle blade angle defined between aplane perpendicular to the free end of the blade at a middle portion ofthe blade and a plane perpendicular to the hub, wherein the distal bladeangle is larger than the middle blade angle, and wherein the middleblade angle is larger than the proximal blade angle.
 2. The impeller ofclaim 1, wherein the distal blade angle is in a range from about 30degrees to about 60 degrees.
 3. The impeller of claim 1, wherein theproximal blade angle is in a range from about 30 degrees to about 45degrees.
 4. The impeller of claim 1, wherein the middle blade angle isin a range from about 25 degrees to about 55 degrees.
 5. The impeller ofclaim 1, wherein the distal, proximal, and middle blade angles areselected to achieve relatively high flow rates at relatively lowrotational speeds.
 6. The impeller of claim 1, wherein the distal,proximal, and middle blade angles are selected to achieve flow ratesgreater than 3.5 liters/minute.
 7. The impeller of claim 1, wherein thedistal blade angle is about 50 degrees, the middle blade angle is about40 degrees, and the proximal blade angle is about 35 degrees.
 8. Acatheter pump comprising: a catheter; and an impeller mounted at an endof the catheter, the impeller comprising: a hub having a proximal endportion and a distal end portion; and at least one blade supported bythe hub, the at least one blade transitionable between a stored positionand a deployed position, the at least one blade having a fixed endcoupled to the hub and a free end, wherein the at least one bladecomprises: a distal blade angle defined between a plane perpendicular tothe free end of the blade near a distal end of the blade and a planeperpendicular to the hub; a proximal blade angle defined between a planeperpendicular to the free end of the blade near a proximal end of theblade and a plane perpendicular to the hub; and a middle blade angledefined between a plane perpendicular to the free end of the blade at amiddle portion of the blade and a plane perpendicular to the hub,wherein the distal blade angle is larger than the middle blade angle,and wherein the middle blade angle is larger than the proximal bladeangle.
 9. The catheter pump of claim 8, wherein the distal blade angleis in a range from about 30 degrees to about 60 degrees.
 10. Thecatheter pump of claim 8, wherein the proximal blade angle is in a rangefrom about 30 degrees to about 45 degrees.
 11. The catheter pump ofclaim 8, wherein the middle blade angle is in a range from about 25degrees to about 55 degrees.
 12. The catheter pump of claim 8, whereinthe distal, proximal, and middle blade angles are selected to achieverelatively high flow rates at relatively low rotational speeds.
 13. Thecatheter pump of claim 8, wherein the distal, proximal, and middle bladeangles are selected to achieve flow rates greater than 3.5liters/minute.
 14. The catheter pump of claim 8, wherein the distalblade angle is about 50 degrees, the middle blade angle is about 40degrees, and the proximal blade angle is about 35 degrees.
 15. Acatheter pump comprising: an expandable cannula; and an impellerpositioned within the expandable cannula, the impeller comprising: a hubhaving a proximal end portion and a distal end portion; and at least oneblade supported by the hub, the at least one blade transitionablebetween a stored position and a deployed position, the at least oneblade having a fixed end coupled to the hub and a free end, wherein theat least one blade comprises: a distal blade angle defined between aplane perpendicular to the free end of the blade near a distal end ofthe blade and a plane perpendicular to the hub; a proximal blade angledefined between a plane perpendicular to the free end of the blade neara proximal end of the blade and a plane perpendicular to the hub; and amiddle blade angle defined between a plane perpendicular to the free endof the blade at a middle portion of the blade and a plane perpendicularto the hub, wherein the distal blade angle is larger than the middleblade angle, and wherein the middle blade angle is larger than theproximal blade angle.
 16. The catheter pump of claim 15, wherein thedistal blade angle is in a range from about 30 degrees to about 60degrees.
 17. The catheter pump of claim 15, wherein the proximal bladeangle is in a range from about 30 degrees to about 45 degrees.
 18. Thecatheter pump of claim 15, wherein the middle blade angle is in a rangefrom about 25 degrees to about 55 degrees.
 19. The catheter pump ofclaim 15, wherein the distal, proximal, and middle blade angles areselected to achieve relatively high flow rates at relatively lowrotational speeds.
 20. The catheter pump of claim 15, wherein thedistal, proximal, and middle blade angles are selected to achieve flowrates greater than 3.5 liters/minute.